EP2626532A1 - Method for operating a gas turbine - Google Patents

Abstract

The method involves partially reforming the fuel gas (B) supplied to a gas turbine (2) before addition of water vapor to the gas turbine, where the reforming takes place in a tubular reactor (60). The tube reactor is heated by the exhaust gases of the gas turbine, where the fuel gas is passed into a heat exchanger (62) before being fed into the gas turbine and after reforming. The addition of water vapor is performed by a jet pump, where the water vapor is taken to a heat recovery steam generator (14) associated with the gas turbine.

Description

The invention relates to a method for operating a gas turbine.

A gas turbine is an internal combustion engine, consisting of the gas turbine in the narrower sense (expander) with an upstream compressor and a combustion chamber in between, to which a fuel gas, typically natural gas is supplied. The principle of operation is based on the Joule process, in which air is compressed via the blading of one or more compressor stages, which is then mixed in the combustion chamber with a fuel gas, ignited and burnt. The result is a hot gas (mixture of fuel gas and air), which relaxes in the subsequent turbine part, with thermal converts to mechanical energy and first drives the compressor. The remaining portion is usually used to drive a generator, a propeller, a rotor, a compressor or a pump. In jet engines on the other hand, the thermal energy accelerates the hot gas flow, which generates the thrust.

Stationary gas turbines are commonly used in gas and steam turbine (GUD) power plants. In the combined cycle power plant, electricity is generated with one to four gas turbines and one steam turbine, whereby either each turbine drives a generator (multi-shaft system) or a gas turbine with the steam turbine (uncouplerable) on a common shaft the generator (single-shaft system). The hot exhaust gases of the gas turbines are used in a waste heat steam boiler for generating water vapor. The steam is then released via a steam turbine process.

GUD power plants are very flexible in power plant management: thanks to short start times and the possibility Fast load changes make them ideal mid-load power plants. These power plants are therefore primarily operated in the middle load range, but if necessary also in the area of the peak current.

However, especially in part-load operation, gas turbines tend to increase CO emissions as a matter of principle. The cause is essentially a reduction of the turbine inlet temperature, with which the desired partial load is set. The burnout and thus the CO emissions are directly related to this temperature reduction. Accordingly, in order to reduce CO emissions, it is often aimed specifically at thermodynamic parameters. So z. As the burner inlet air mass flow can be reduced (by blowing off compressor air in front of the combustion chamber or reducing the intake air mass flow by closing the compressor guide vanes), the turbine inlet temperature can be increased by raising the exhaust gas temperature or the compressor inlet temperature can be increased associated with a reduction of the Ansaugmassenstroms.

Depending on the legal framework, the continuous operation of the gas turbine is nevertheless limited to low loads. Below these minimum loads, the power plant operator only has to shut down the system. Restarting with sufficient demand for power is quickly possible, but generally costs the life of the thermally stressed components.

It is therefore an object of the invention to specify a method for operating a gas turbine, which allows a further increase in operational flexibility, in particular in the partial load range with simultaneously low CO emissions.

This object is achieved according to the invention by partially reforming the gas turbine supplied fuel gas before the supply to the gas turbine with the addition of water vapor.

The invention is based on the consideration that an increase in operational flexibility and low CO emissions in the partial load range could be achieved by improving the burnout of the fuel gas. The burn-out is influenced by design-related and process-related variables. Essentially, these are mixing, quenching effects when mixed with cooling air streams, the available residence time in the combustion chamber and the fuel properties. In addition to the already known thermodynamic measures could therefore be a constructive increase in the residence time z. B. reduce the CO content by increasing the length of the combustion chamber. However, this has a negative effect on the NOx emissions at high combustion chamber temperatures, so that this option is eliminated.

Therefore, a modification of the fuel properties should be made, i. H. If necessary, the fuel composition should be changed to reduce CO emissions. This is particularly easy possible, in which the fuel gas is partially reformed with the addition of water vapor. The resulting mixture of carbon monoxide, hydrogen, natural gas and water has an increased reactivity, which accelerates the burnout of the carbon monoxide formed in the flame front.

In an advantageous embodiment, the reforming is carried out in a tubular reactor, the fuel gas is supplied to the previously added steam. The tubular reactor is particularly well suited to provide the temperature and pressure parameters required for reforming. The reforming can be operated both with and without a catalyst.

In a further advantageous embodiment of the tubular reactor is heated by means of the exhaust gases of the gas turbine. The heating of the tubular reactor can either be done directly with gas turbine exhaust gas or the tubular reactor is located at a suitable point in one of the gas turbine downstream heat recovery steam generator. This is particularly efficient, since no additional heating is necessary. The exhaust gases provide a temperature of about 400 to 650 ° C available. Although these temperatures may not be sufficient for a complete reforming of the fuel gas. However, a full implementation is not required for the application in a gas turbine and also not desirable. Rather, sufficient enrichment with hydrogen, so that the reactivity is increased, on the other hand, but no risk of operation by flashback arises.

Advantageously, the fuel gas is passed before being fed to the gas turbine and after reforming in a heat exchanger. As a result, the heat content of the reformed fuel gas can be used to increase efficiency, for example, to generate steam or to preheat the fuel gas.

Advantageously, the addition of water vapor by means of a jet pump, wherein the water vapor is used as a driving medium and the fuel gas is used as the suction medium. As a result, in particular in comparatively higher load ranges in which the pressure of the fuel gas is no longer sufficient to compensate for the pressure losses in the mixer and tubular reactor, a sufficient pressure for the reformed fuel gas can be generated.

In this case, the steam is advantageously taken from a waste heat steam generator associated with the gas turbine. This steam typically has a comparatively high pressure, which can be advantageously used to increase the pressure of the reformed fuel gas and / or the use in a jet pump.

Advantageously, the gas turbine is operated below 70% of its maximum power. Especially in such comparatively low load ranges, it is possible to operate the gas turbine still emissions compliant by reforming the fuel gases.

Advantageously, a gas turbine is operated with the described method and a power plant comprises such a gas turbine.

The power plant is advantageously designed as a gas and steam turbine power plant. As a result, multiple synergy effects can be achieved with respect to the method described. So z. B. the water vapor can be used from the steam cycle.

The advantages achieved by the invention are in particular that by the partial reforming of the fuel gas with supply of water vapor even at low loads of a gas turbine, d. H. At reduced flame temperatures and the typical residence times available in gas turbine combustors, carbon monoxide has reacted to below the required limit values. As a result, the gas turbine can continue to operate even at low loads and there is no life-reducing and startup necessary. The process control with the parameters residence time and steam / natural gas ratio is to be dimensioned so that a safe operation without flashback is possible with the designed for natural gas operation burners.

The reformed fuel gas can be mixed either into the main gas stream, the premix gas stream, into the pilot gas stream or specifically into individual combustion stages. Due to the restriction to individual combustion stages, even with low mass flows one obtains a clear influence on the emission data.

Overall, it is possible with the described method to specifically influence the reactive properties of the fuel and to adapt to the requirements of emission data and combustion stability in the partial load range. This makes it possible to operate gas turbines in accordance with the emissions even at low loads.

• FIG 1 eine schematische Darstellung eines Gas- und Dampfturbinenkraftwerks mit einer Gasturbine mit Brenngasreformierung mit Mischeinheit zur Vermischung von Wasserdampf und Brenngas, und
• FIG 2 eine schematische eine schematische Darstellung eines Gas- und Dampfturbinenkraftwerks mit einer Gasturbine mit Brenngasreformierung mit Strahlpumpe zur Vermischung von Wasserdampf und Brenngas.

The invention will be explained in more detail with reference to a drawing. Show:

• FIG. 1 a schematic representation of a gas and steam turbine power plant with a gas turbine with fuel gas reforming with mixing unit for mixing water vapor and fuel gas, and
• FIG. 2 a schematic a schematic representation of a gas and steam turbine power plant with a gas turbine with fuel gas reforming with jet pump for mixing water vapor and fuel gas.

Identical parts are provided with the same reference numerals in all FIGS.

The combined cycle power plant 1 according to the FIG. 1 includes a gas turbine 2 and arranged with the gas turbine 2 on a common shaft 4 generator 6. The combined cycle power plant 1 is designed as a single-shaft system. On the shaft 6, therefore, a steam turbine 8 is arranged. The steam turbine 8 is designed for a simple reheat, thus comprises three turbine stages, namely one high, medium and low pressure stage.

The steam cycle begins with the preheating of the feedwater in the preheater 10, which, like all the preheaters, evaporators and superheaters described below, are arranged in a waste heat steam generator 14 connected downstream of the exhaust gas channel 12 of the gas turbine 2. The preheated feed water is distributed from there to the low-pressure steam drum 16 and the feedwater pump 18. From the feedwater pump 18, the feedwater is in turn passed through the medium-pressure preheater 20 in the medium-pressure steam drum 22 and parallel to the high-pressure preheater 24.

The high-pressure part of the heat recovery steam generator 14 is designed in the passage, d. H. There is no steam drum. Rather, the medium from the high pressure preheater 24 is passed directly into the combined high pressure evaporator and superheater 26. From there, it flows into a water-vapor separator 28, which ensures essentially only at low loads for a separation of remaining liquid medium. The steam from the water-steam separator 28 is reheated in the high-pressure superheater 30 again and then fed via the high-pressure steam line 32 of the high-pressure stage of the steam turbine 8.

The middle and low pressure stages of the heat recovery steam generator 14 are designed in circulation. Starting from the low pressure steam drum 16 is circulating, d. H. The low-pressure evaporator 34 flows through in a circulating manner, analogously to the medium-pressure steam drum 22, starting from the medium-pressure evaporator 36. The steam accumulating in the steam drums 16, 22 is conducted into the low-pressure superheater 38 or the medium-pressure superheater 40. With the steam from the low-pressure superheater 38, the low-pressure stage of the steam turbine 8 is fed via the low-pressure steam line 42.

By contrast, the steam from the medium-pressure superheater 42 is mixed with the steam which has been expanded in the high-pressure stage of the steam turbine 8 and returned via the return line 44 and fed into the reheater 46. From here, the steam is fed via the medium-pressure steam line 48 to the medium-pressure stage of the steam turbine 8. In the steam turbine 8 incidentally accumulating steam is passed into the condenser 50, where it is liquefied and fed back to the feedwater pump 18 via a condensate pump 52 and the feedwater line 54.

The gas turbine 2 is acted upon by natural gas as fuel gas B. The resulting in the gas turbine 2 exhaust gas is passed after the passage of the heat recovery steam generator 14 in a chimney 56 and from there into the environment. Accordingly, here are To comply with limit values with regard to the CO content of the exhaust gas. In order to ensure this even at low loads, the fuel gas B or optionally a part of the fuel gas B is fed to a mixing unit 58, in which it is mixed with extracted in the region of the medium pressure superheater 40 steam. The water vapor / fuel gas mixture is then fed to a tubular reactor 60 arranged in the heat recovery steam generator 14.

In the tubular reactor 60, the gas is partially reformed by the pressure prevailing there and the temperature prevailing there. The partially reformed fuel gas is then passed into the burners of the gas turbine 2 via a heat exchanger 62, in which the fuel gas B previously supplied to the mixing unit 58 is preheated. In an alternative, not shown embodiment, the heat exchanger 62 is connected in the feedwater line 54.

The embodiment according to FIG. 2 is only based on their differences to FIG. 1 described. The mixing unit 58 is here replaced by a jet pump 64. The steam is taken from the water-steam separator 28 of the high pressure stage of the heat recovery steam generator 14 and acts as a propellant in the jet pump. Thereby, the pressure of the reformed gas is increased and the embodiment according to FIG. 2 is also suitable for higher loads of the gas turbine 2.

Claims (10)

Method for operating a gas turbine (2),
in which the fuel gas (B) supplied to the gas turbine (2) is partially reformed before it is fed to the gas turbine (2) with the addition of water vapor. Method according to claim 1,
in which the reforming is carried out in a tubular reactor (60), the fuel gas (B) is supplied to the previously added steam. Method according to claim 2,
in which the tube reactor (60) is heated by means of the exhaust gases of the gas turbine (2). Method according to one of the preceding claims,
in which the fuel gas (B) before feeding to the gas turbine (2) and after reforming in a heat exchanger (62) is passed. Method according to one of the preceding claims,
in which the addition of water vapor by means of a jet pump (64), wherein the water vapor as a driving medium and the fuel gas (B) is used as a suction medium. Method according to claim 5,
in which the steam is taken from a waste heat steam generator (14) associated with the gas turbine (2). Method according to one of the preceding claims,
in which the gas turbine (2) is operated below 70% of its maximum power. Gas turbine (2),
operated by the method according to any one of the preceding claims. Power plant (1) with a gas turbine (2) according to claim 8. Power plant (1) according to claim 9,
which is designed as a gas and steam turbine power plant (1).

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